By Robert Nisbet BBC Entertainment correspondent

She only came up to the knees of most of the gun-toting security staff surrounding the US treasury secretary, but little Pearl stuck doggedly to her task.

Swept along by the media scrum, which squeezed its way through the Ghana market's dark and narrow alleyways, the little girl made sure she stayed just inches away from the two men at its centre.

Bono switches from fronting a band to fronting an aid message

Her patience was eventually rewarded.

As the shutters snapped and the tapes rolled, a rock star and one of the world's most powerful men squabbled over who would buy her a necklace.

It was one of many photo opportunities in the market which, even at seven in the morning, was beginning to absorb the humidity of a May day in Accra.

The U2 frontman Bono looked slightly more comfortable in the heat as he chatted with stallholders, stopping to buy a bag of peppers, while the US Treasury Secretary Paul O'Neill blended in as best he could, decked out in a freshly pressed Oxford shirt, spotless leisure slacks and immaculate loafers.

Despite their obvious differences (one made his money out of aluminium, the other out of rock) the two were soon absorbed trying to convince the other of how best to help Africa's poorest nations.

For Bono, it is a mix of debt cancellation, short-term aid and helping African exporters achieve a fairer price for their products.

Bono's desire

Mr O'Neill, on the other hand, is a free wheeling free trader, who thinks Africa should throw open its markets to foreign investors.

It's been a hard day's night for Bono

Bono regards the poorer countries as unfortunate losers in a global game of risk, Mr O'Neill sees them more as businesses in need of serious tinkering at boardroom level.

The gulf between them is reflected in the media surrounding them, with a crowd of be-tied Washington-based economic journalists in one coach, and a rabble of jeans-clad entertainment reporters in the other.

Bono manages to keep both engaged. On the first day of the tour, we returned to the La Palm hotel after a busy schedule which involved trade fairs, a visit to the sumptuous castle which houses Ghana's President John Kufuor.

Not forgetting round table discussions with community leaders and a tribal king who entered the room preceeded by a page carrying a large pink umbrella and another blowing on a conch shell, before challenging everyone's preconceptions by speaking in an American accent.

With or without you

As soon as Bono walked into the lobby, the exhausted singer was surrounded by the financial journalists, exploring the strength of his grip on macroeconomics.

US Treasury Secretary sees the funny side

He parried their questions successfully until he started to weaken. Leaning over to me (spotting that I fell in to the light entertainment category) he asked, under his breath, to be dragged to the bar, under the guise of a pre-arranged interview.

I complied. Two large gin and tonics later, and we were talking about his early days in London on the Chiswick Road while he puffed on the cigarette he had begged off an astonished couple sitting nearby.

The force of Bono's personality certainly gets him noticed, but the force of his argument means he is also taken seriously.

Though many, including Paul O'Neill, quibble with major parts of his solution, which he describes as a "partnership" between the richer countries in the north and the poorer ones in the south, his involvement has ensured this trip to Ghana, South Africa, Uganda and Ethiopia is getting so much attention.

Beautiful day

Certainly the travelling press corps will find it hard to forget.

Especially those of us who drank bottles of beer and ate army rations while trapped for 8 hours in the northern town of Tamale, waiting for the storm clouds to clear for our return flight to Accra.

Bono entertained us with magic tricks which became increasingly less convincing as the crates of beer emptied.

The sight of Bono staggering across the tarmac with his entourage while Paul O'Neill strode purposefully - and soberly - up the steps to the presidential jet accentuated the difference between the two men, but was also strangely reassuring.

The rock star hadn't given up his day job.